Operating any aircraft outside of the operational limits will result in structural damage or difficulty in aircraft control. It is very especially important that you, as the PIC, calculate and manage the weight and balance, to ensure the aircraft is in safe operation and within limits.
A few Terms and Definitions we need to know before getting started.
Center of Gravity (CG) - The point at which the aircraft would balance if it were suspended at that point.
Datum - An imaginary line from which all measurements of the arm are taken.
Arm - The horizontal distance in inches from the reference datum line to the CG
Moment - Equals the weight x the arm.
Basic empty weight - the standard empty weight plus the weight of special equipment, paint, etc. that have been added. This number is found on the weight and balance sheet for the aircraft.
One number we need known for calculation is the weight of fuel.
Aviation gas (AVGAS) - 6 pounds per gallon.
Think of an airplane as a seesaw, and the pivot point of the seesaw is the center of gravity (CG). The CG is the point at which all the weight is concentrated.
If too much weight is too far forward (forward CG) the nose of the aircraft becomes difficult to raise. Whereas if there is too much weight in the aft (aft CG), the aircraft is less stable, and tends to stall and recovery becomes difficult.
The forward and aft CG are referenced from the datum line. The datum line is established by aircraft manufactures and varies in location. The distance from the datum to any component part or any object loaded on the aircraft is called the arm.
When the object or component is located aft of the datum, it is measured in positive inches; if located forward of the datum, it is measured in negative inches. The location of a component in inches is also referred to as station number.
If the weight of any object or component is multiplied by the distance from the datum (arm), the product is the moment.
(Weight x Arm = Moment)
How to fill out a weight and balance
It is not necessary to fill one out if flying to the practice area or flying on a short solo flight to a near by airport. However, figuring out the weight and balance should be good practice and completed prior to flying with family or friends on a cross-country flight, any overnight stay, or carrying a large load.
NOTE: A blank Weight and Balance form can be downloaded here.
All the weight and balance charts and tables are found in the aircraft POH.
To calculate the weight and balance we need to first find the Basic Empty Weight of the aircraft. This is found in the aircraft’s weight and balance sheet. Each aircraft has its own individual sheet that is filled out every time something gets removed or installed by an aircraft mechanic.
Next, we need to determine the weight of each person, baggage and fuel that will be loaded on the aircraft.
3. To find the Arm simply take the Weight and divide it by the Moment.
4. Once every block is filled out, add up all the weights to find the total. Then add up all of the moments to find the total and check to see if the airplane is within limits per the loading chart, shown above.
In the example on figure 2, the airplane is well within the Normal Category as shown on figure 3, represented by the star.
Remember:
The Basic Empty Weight of the aircraft is found in the aircraft’s weight and balance sheet.
Moment - Equals the weight x the arm. (To find the Arm simply take the Weight and divide it by the Moment).
Aviation gas (AVGAS) - 6 pounds per gallon.
All the weight and balance charts and tables are found in the aircraft POH.
References:
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